1. Field of the Invention
This invention relates to pneumatically operated apparatus and systems for driving fasteners.
2. Description of Prior Art
Pneumatic fastener driving tools are widely used in the building industry to join structural components together. The tools commonly employ a piston type drive mechanism which, during its driving stroke, engages one of a series of fasteners fed to the tool to force the fastener into the components to be joined.
Various attempts have been made to use pneumatic tools of this type as nailers to secure drywall sheets to framing studs in the construction of walls. In the fastening of drywall or other wallboard sheets to wooden framing studs, three criteria must typically be met for approval of the wall construction under applicable building codes and to provide a smooth finished wall surface. First, the head of each of the driven drywall nails must be recessed in the drywall to a depth within a specified range. Secondly, it is necessary or desirable to dimple or slightly recess the drywall around the recessed heads of the driven nails so that the nail heads can be concealed with spackling or the like subsequently deposited in and around each of the dimples. Thirdly, each of the mounted drywall sheets must be held in firm abutment with each of its framing studs at each nail location.
Several pneumatic tools have been proposed to perform these multiple functions in a single operation--i.e., to simultaneously drive the nail and properly recess its head, form a dimple in the drywall around the nail head, and ensure a firm abutment between the drywall sheet and its supporting studs at each nail location. However, none of these prior art tools has satisfactorily accomplished these multiple functions.
The chief reason for the failure of conventional pneumatic fastener drivers to satisfactorily drive, recess, dimple and secure in one operation is that they recoil away from the drywall at the instant they are actuated. This heretofore unavoidable recoil renders it difficult to control the depth of either the nail recess or the dimple since as the nail-driving and dimpling mechanisms are being driven toward the drywall, the tool itself is being reactively thrust away from it. The nail recess and dimple depths are thus functions of the force with which the tool's operator presses it against the drywall during firing to limit recoil.
Therefore, with conventional fastener driving tools, the achievement of uniform recess and dimple depths usually requires a rather high degree of skill and experience on the part of the tool's operator. Too little contact pressure between the conventional tool and the outer drywall surface results in unacceptably shallow nail recesses and dimples (or the lack thereof) while excessive pressures can cause breakage of the drywall. Either situation can result in rejection of the resulting wall structure by a building inspector, and the necessity to rebuild it.
Tool recoil upon actuation can also cause loose connection points between drywall and studs (and, thus, a similar rejection of the wall by a building inspector) even though proper nail recesses and dimples have been formed. It is usually the case that the nailing surfaces of the studs (i.e., the surfaces which the inner surfaces of the installed drywall sheets must abut) are neither perfectly flat nor exactly coplanar. Thus, at many nail locations, a gap exists between the stud nailing surface and the inner surface of the drywall prior to the driving of nails at such locations. If the drywall is not pushed inwardly and held firmly against the stud while a nail is being driven into the stud, at least a portion of this gap remains after the nail is driven and the spackling is applied to its surrounding dimple. Subsequent inward pressure against the drywall (for example, when it is inadvertently bumped) can cause inward movement of the drywall relative to the stationary nail which causes the nail's head to pop the spackling out of its dimple and ruin the wall's finish.
To prevent this from occurring, it is necessary to press the tool against the drywall until the drywall is forced firmly against the underlying stud, and maintain the drywall-stud contact until the nail is completely driven. As in the case of trying to achieve uniform nail recess and dimple depths, this is made difficult by the rearward recoil of conventional pneumatic nailers at the instant of their actuation. If considerable pressure is not maintained between the tool and the drywall during firing, such firing recoil allows the drywall to spring out from the stud during firing so that the driven nail does not hold the drywall firmly against the stud.
Another problem associated with conventional pneumatic fastener drivers involves the nailing of drywall at the corners of a room. At the typical room corner, each of the drywall nails must be positioned less than an inch from the adjacent wall. With this rather small distance, it is difficult to provide a tool having sufficient power so that it is capable of accurately and forcefully driving a nail into the underlying studding while simultaneously forming a proper dimple in this awkward location.
Conventional pneumatic nailers are not noted for their durability. Particularly when such tools are inadvertently "dry fired" (i.e., when they are fired without adequate backup such as a framing stud), their fastener-driving and dimpling mechanisms are subjected to high stresses which cause rather rapid component fatigue and failure necessitating repairs and equipment downtime. This problem is particularly acute in tools in which there is metal-to-metal contact during either regular or dry firing of the tool.
In order to permit the nailing of a series of nails or other fasteners successively by an automatic tool, it has been previously proposed to secure the fasteners together in a "collation" of flexible assembly in which the nails or other fasteners are positioned in a row for successive pickup and use by the automatic fastening tool. Conventional collations involve the complete enclosing of a portion of each of the fasteners by the plastic or wire typically used to join the fasteners and form the collation assembly. Accordingly, when the fastener is driven into the wall or other parts to be joined, a portion of the plastic or wire joining material is frequently sheared off and embedded in the wall or other components, tending to mar the finished structure or otherwise diminish the consistency and effectiveness of the fastening process.
Accordingly, it is an object of the present invention to provide a pneumatic fastener driving tool which eliminates or minimizes above-mentioned and other problems.